I just replaced my impeller and thermostats back in April and all was well till I just took it out last week and noticed it was running a little hot. It's a '96 Merc 150 EFI. It seems to be pumping good. Could this be caused by the high lake water temps? It runs a little hotter at WOT than at idle, but either way the gauge reads a little over half way. I've ordered a poppet valve and am going to replace that too just in case, but otherwise I don't know what else it could be. Any ideas?

What do you mean by a little hot. Many times you can actually see better WOT water pressure by closing off the top 2 water intake ports on both sides of the lower unit. I use Permatex black RTV. The warmer lake temps definitely have an effect on everything.

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What do you mean by a little hot. Many times you can actually see better WOT water pressure by closing off the top 2 water intake ports on both sides of the lower unit. I use Permatex black RTV. The warmer lake temps definitely have an effect on everything.

generic temp gauges just give ya something for a "guess" at being hot or cold.. a temp gun will tell ya at what temps are (only true way of knowin' what actual temps are) and can be compared to where tha gauge is reading.. other than that as long as tha over temp sensor and buzzer are workin' should be good...

thats why "temp gauges" are usually an option (or use ta be).... probably used as a "sellin' point" nowdays...